Once you've spent time weighing the costs and benefits of your
first purchase and decide to go for it, a psychological trigger
switches on, meaning you've entered the buying phase.

"Once that happens, a roller roaster of shopping can begin," said
Uzma Khan, a head researchers on the study.

The momentum only increases the longer you're in the store, which
helps to explain why stores position practical items like
newspapers or umbrellas toward the front of their shops. In other
words, they're brainwashing you.

Consumers will grab the items as they head to the register, and
once someone decides to buy that newspaper, for example, the
shopping momentum makes him that more likely to pick up a guilty
pleasure like a chocolate bar.

That's also why stores have fewer checkouts, with most registers
in the same section. It gives people less of an opportunity to
deliberate, allowing the momentum to run its course. Ka-ching!